Study of samples of a material, e.g. rock, may require observation of structural changes which occur under various types of treatment of a sample. Typical treatments include: multiphase filtering of gas, liquid and solids through a sample, chemical treatment, mechanical treatment (deformation), heating, cooling, diffusion, etc. Generally, a treatment modifies either a structure of the sample or a distribution of substances within pores of the sample.
Transportation or storage of a sample is also an example of treatment, since the sample may undergo changes.
Usually, changes occurring in samples are defined using values of changes in various bulk properties (physical dimensions, weight, density, porosity, etc.). A variety of methods for determining these properties are known. For example, porosity can be measured by measuring pressure versus gas flow rate in the sample saturation process through weighing the liquid-saturated sample or petrographic analysis of sections (U.S. Pat. Nos. 4,562,726, 2,840,717). It is apparent that to evaluate changes in the sample these methods should be applied twice—before and after sample treatment.
Variation in wettability of a sample due to changes in physical properties of pore surface can be measured by the Amott method (D. Tiab and E. C. Donaldson, “Petrophysics: Theory and Practice of Measuring Reservoir Rock and Fluid Transport Properties”, Gulf Professional Publishing, 2nd Edition, 371-373 (2004)). The method substantially relies on the capillary displacement of water from a completely water-saturated sample by a liquid hydrocarbon mixture (kerosene), followed by displacement of the hydrocarbon mixture from the sample by water. The main disadvantage of this method is its low sensitivity, near neutral values of wettability and a high measurement error in the case of small samples, where the results of measurements of bulk properties become comparable with the measurement error of the methods.
Furthermore, the aforementioned and similar methods have other disadvantages:                Lack of spatial resolution        Inability to determine the immediate cause of changes that occurred        Low sensitivity to small changes in the sample—the measurement error may be greater than the required difference between the measured values.        Damage of the sample during measurements, which may hinder detection of changes due to the effect under investigation.        